Powdered thermoplastic polyolefin composition having resilient properties

ABSTRACT

A thermoplastic polyolefin composition having resilient properties is provided for producing interior trims for motor vehicles by slush moulding. The composition contains (a) around 95-5 parts by weight, preferably 97-10 parts by weight of a matrix consisting of at least one polymer containing at least 50 mol % of propylene and at least one at least partially cross-linked polyolefin elastomer; (b) around 3-95 parts by weight, preferably 5-90 parts by weight of at least one polymer containing at least 50 mol % of ethylene; and (c) 0-6 parts by weight of an internal release agent per 100 parts by weight of components (a) and (b).

FIELD OF THE INVENTION

The invention relates to a polyolefin thermoplastic composition havingelastic properties, being in the form of fine particles conferring on itthe character of a powder.

The invention relates more especially to a polyolefin thermoplasticcomposition having elastic properties, being in the form of a powder,for the production of skins by the process of powder slush moulding onconventional equipment.

The invention also relates to the process for preparing the saidcomposition.

Finally, the invention relates to the moulded articles produced by theuse of the composition.

TECHNICAL BACKGROUND OF THE INVENTION

Many components made of polymer materials are increasingly being used inthe construction of motor vehicles: such as dashboards, door panels,consoles, etc. Some of them are used very visibly in the internalarchitecture of the vehicle, in such a way that they must have, on thevisible surface, a pleasing aesthetic appearance which reproduces, forexample, the appearance of leather. This visible surface constitutes theskin of the component. This skin, bulk coloured, must also have otherproperties, which are good scratch resistance and good resistance tochemicals such as solvents, as well as the ability to withstand thermalvariations, ranging from the very cold to the prolonged exposure tosunshine in a confined atmosphere.

The abovementioned skin may concern all components (also called inserts)made of polymer materials, particularly those involved in the internalarchitecture of the vehicle—from the rigid inserts generally reservedfor bottom-of-the-range vehicles to the foamed inserts with which moresophisticated vehicles are equipped.

In the case of rigid inserts, the skin, or at very least its appearance,is obtained by the etching of the mould, either as a result of theconstituent material of the insert or else, for example, by theco-injection moulding of two different materials, one for the insert andthe other for the skin.

In the case of foamed inserts, the skin is generally made, independentlyof the insert itself, of a material compatible, on the one hand, withthe foam subsequently developed between the said skin and the insertand, on the other hand, with the finishing lacquers, such aspolyurethane lacquers, deposited on the visible surface of the said skinin order to make them comply, where necessary, with the specificationsof motor-vehicle manufacturers.

In order to produce the skin of inserts, such as the dashboard forexample, various processes have been proposed, one of the preoccupationsof which is to produce a skin with the lowest possible residual stress.

In a first type of process which uses a premanufacturedpolypropylene-based sheet, the skins of dashboards are produced by meansof the process of positive or negative thermoforming. However, thethermo-forming employed, whether positive (the surface appearance of theskin exists on the sheet before thermoforming) or negative (the surfaceappearance is given to the sheet by the mould during thermoforming),generally involves, both for technical and economic reasons, sheets(preheated) which are preferably thin. Consequently, the shapes of theskins obtained are very limited and contain residual stresses which,when they are relieved by ageing, generate crazes which are veryunattractive.

In one type of process, the skins of dashboards are produced using theslush moulding process (mentioned above) which generally allows them tobe obtained free of residual stresses. By itself, the slush mouldingprocess is a moulding process using conventional equipment(electroformed nickel mould heated by a hot-air system) which allows theproduction of the desired skins using a polymer powder based onpolyvinyl chloride (PVC) by the technique of powder slush moulding. Theskins thus produced, although they no longer include residual stresses,or very few residual stresses, and although they meet for the most partthe specifications of motor-vehicle manufacturers, do have immediate orpotential drawbacks, even in the short term.

Among the immediate drawbacks, the PVC-based skins are quite highlyloaded, owing to their composition, with volatile substances (inparticular, PVC plasticizers). These materials, in use and due to theeffect of temperature variations in the passenger compartment of thevehicle, are volatilized and migrate to cold areas, where theycondense—this is the well-known phenomenon of slow opacification of thewindscreen of a vehicle, which is a particular impediment to thedriver's view and to the proper control of the vehicle.

Among the potential drawbacks, the use of PVC appears, in the currentsituation of end-of-life recycling of materials used in the manufactureof motor vehicles, to be prohibited in the relatively short term forbetter environmental protection.

Polymer materials resulting from grinding up worn-out vehicles arecurrently used (completely or partly) as fuel in certain types offurnaces, such as, for example, furnaces in cement works. However, PVCconverted into a fuel material emits, when it is burnt, acid-gaseffluents which are harmful to the environment.

This is why, in order to meet the twin concern of motor-vehiclemanufacturers and the public authorities, which is firstly that ofprotecting the environment (removing harmful gaseous effluents generatedby the combustion of waste made of polymer materials and limiting thedumping thereof) and then that of more completely recycling the waste(formed from polymer materials) resulting from the destruction ofworn-out vehicles by grinding, motor-vehicle manufacturers seriouslyenvisage limiting the number of polymers present in each vehicle, but atthe same time increasing their relative amounts, and in particularsubstituting PVC with polyolefins in order to allow easier recycling.Thus, motor vehicles would be equipped with components, such as foameddashboards, whose skin, foam and rigid insert would be made ofpolyolefins which can be recycled at the end of the life of thevehicles.

To do this, polyolefin thermoplastic compositions have already beenproposed.

By way of example, document EP 0,508,801 describes a powder compositionof thermoplastic elastomers for powder moulding, which comprises:

either (i) a powder of a thermoplastic elastomer comprising acomposition composed of an ethylene-alpha-olefin copolymer rubber and ofa polyolefin resin;

or (ii) a powder of a thermoplastic elastomer comprising a partiallycrosslinked composition composed of an ethylene-alpha-olefin copolymerrubber and of a polyolefin resin,

this powder composition being able to be used in the slush mouldingprocess.

However, according to this document:

in order to increase melt flow and at the same time to improve theflexibility of the moulded article, the olefin copolymer rubber isdiluted with oil and thus comprises an ethylene-alpha-olefin copolymerrubber with the addition of a mineral oil as a flexibilizer with arelatively high content with respect to the polyolefin elastomer. Theseoils constitute, in fact, a risk of emitting volatile substances whichpollute the environment and opacify vehicle windscreens, and also a riskof impairing the appearance of the skin during its ageing—the phenomenonof exudation is not eliminated.

finally, in order to allow the skin to be easily demoulded, externalmould-release agents (for example, dimethylsiloxane) deposited on themould or mould-release agents internal to the composition.

(for example, methylpolysiloxane) are employed: they also constitute arisk of directly polluting the environment of the manufacturingworkshops, but above all they make it more difficult to carry out thesubsequent operation of lacquering the skins, this currently beingnecessary in order to make them comply with the specifications ofmotor-vehicle manufacturers (appearance, matt-gloss level, scratchresistance, abrasion resistance and resistance to chemicals, includingsolvents).

Another document, U.S. Pat. No. 5,302,454, also describes athermoplastic polyolefin composition, having elastic propertiesutilizable in the automotive field, which is in a pulverulent form.

This composition includes three components:

the first being polypropylene (isotactic index of between 95 and 98) ora copolymer of propylene and of ethylene and/or of an alpha-olefin ofthe CH2═CHR type where R is an alkyl radical having from 2 to 6 carbonatoms, containing more than 85% by weight of propylene and having anisotactic index of greater than 85;

the second being a fraction of an ethylene-containing polymer (insolublein xylene at room temperature);

the third being a fraction of an amorphous ethylene-propylene copolymercontaining from 40 to 70% by weight of ethylene (soluble in xylene atroom temperature).

However, such a composition appears not to be able, except by makingcertain modifications by adding special agents such as, for example,polyolefin resins, to be easily processed in the slush moulding process(risk of clumping and difficulty in demoulding).

Finally, another document, European Patent Application published underthe number EP 0,637,610, describes a process and a thermoplasticpolyolefin composition used in slush moulding for the manufacture ofarticles (laminating) which is in pulverulent form.

This composition includes three fractions:

the first (10 to 40 parts by weight) is a propylene homopolymer or acopolymer of propylene with ethylene and/or a C4 to C10 alpha-olefin;

the second (0 to 20 parts by weight) of a copolymer of ethylene and ofpropylene and/or a C4 to C10 alpha-olefin;

the third (50 to 80 parts by weight) of an elastomeric copolymer ofethylene and of propylene and/or a C4 to C10 alpha-olefin and optionallywith a minor quantity of a diene.

According to this document, the desired intrinsic viscosity of thepolymer composition used in the process in question may be obtained:

either directly by polymerization, controlled by agents for regulatingthe molecular weight;

or by subjecting the polymer composition to a “visbreaking” action whichconsists in cutting the molecular chains present by means of a peroxide.

Such a polymer composition has the same drawbacks as those mentionedpreviously.

Consequently, the problem of using polyolefin compositions assubstitutes for polyvinyl chloride in the production of skins for thefoamed or non-foamed covering of the inserts remains almost in itsentirety.

Thus, the objectives of the invention are to provide a polyolefincomposition having elastic properties, for the production of skins,which:

is in the form of a readily pourable fine powder, to be used in theslush moulding process;

has a substantially improved melting behaviour when it is in contactwith the hot mould;

when being used, provides the skins with all the characteristicsrequired by the functional specifications of motor-vehiclemanufacturers, in particular good thermal, scratch and abrasionresistance and good resistance to chemicals including solvents;

allows the formation of skins having no residual stresses;

is compatible with the subsequent lacquering operations, should thislacquering be necessary;

does not contain agents having high vapour pressures;

does not manifest whitening phenomena at reverse tapers duringdemoulding or during subsequent handling of the skin;

allows excellent demoulding of the component formed;

can be completely recycled, after use, within the motor-vehicle productline in order to meet the environmental protection requirements; and

meets the technical and economic requirements.

SUMMARY OF THE INVENTION

Aware of the above drawbacks, the Applicant has sought, through itsresearch, to obtain a pulverulent polyolefin composition meeting theobjectives that it has set itself.

According to the invention, the polyolefin thermoplastic compositionhaving elastic properties, intended for the production of skins by slushmoulding, being in the form of powder, which contains fractions, onebeing formed of a polypropylene-based homopolymer or copolymer, anotherbeing formed of an ethylene-based copolymer and the final one beingformed of an elastomer, is characterized in that it is composed of:

a) from 97 to approximately 5 parts by weight and preferably from 95 to10 parts by weight of a matrix composed of at least one polymercontaining at least 50 mol % of propylene and of at least one at leastpartially crosslinked polyolefin elastomer;

b) from 3 to approximately 95 parts by weight and preferably from 5 to90 parts by weight of at least one polymer containing at least 50 mol %of ethylene; and

c) from 0 to 6 parts by weight of an internal mould-release agent per100 parts by weight of components “a” and “b”.

DETAILED DESCRIPTION OF THE INVENTION

Thus, the invention relates to a pulverulent polyolefin compositionhaving elastic properties, processed using the slush moulding process,for the manufacture of skins, the desired essential characteristic ofwhich is to have good melting in contact with the mould, preferablybetween 200° C. and 240° C.

But the invention also relates to a process for preparing thiscomposition and to the articles moulded by processing the saidcomposition.

According to the invention, the thermoplastic polyolefin compositionhaving elastic properties firstly comprises a polymer matrix. Thispolymer matrix constituting component “a” of the composition is a blendwhich comprises at least one thermoplastic polymer containing at least50 mol % of propylene and at least one at least partially crosslinkedpolyolefin elastomer.

The thermoplastic polymer containing at least 50 mol % of propylene usedin component “a” may be polypropylene itself (the semicrystallinehomopolymer) or else a semicrystalline propylene-ethylene copolymer, ablend of a semicrystalline homopolymer polypropylene and ofsemicrystalline propylene-ethylene copolymer, mentioned above, or else(homopolymer) polypropylene having amorphous and semicrystalline blocks,and propylene-ethylene or alpha-olefin copolymers having amorphous andsemicrystalline blocks.

The semicrystalline propylene-ethylene copolymer used in component “a”contains small quantities of ethylene, generally lying between 2% and5%, expressed by weight, so that essential properties, like the ease ofprocessing by lowering the melting point of the matrix, the absence ofwhitening under impact and when folded and the ease of demoulding in thecase of components with a reverse taper, are acquired.

The at least partially crosslinked thermoplastic polyolefin elastomerused in the composition of the matrix constituting component “a” may bechosen from thermoplastic elastomers:

used alone, such as: ethylene-propylene rubber (EPR),ethylene-propylene-diene monomer (EPDM), styrene-butadiene-styrene(SBS), styrene-ethylene-butadiene-styrene (SEBS), styrene-butadienerubber (SBR), this being at least partially crosslinked;

or used as a blend, either in a reactor or by extrusion, ofpolypropylene with at least one elastomer, such as, for example,polypropylene/ethylene-propylene rubber (PP/EPR),polypropylene/ethylene-propylene-diene monomer (PP/EPDM), theelastomeric fraction of which is at least partially crosslinked.

The matrix of the polyolefin thermoplastic composition according to theinvention is composed of, expressed in % by weight:

from 5 to 95% and preferably from 80 to 20% by weight of at least onepolymer containing at least 50 mol % of propylene; and

from 95 to 5% and preferably from 20 to 80% by weight of at least one atleast partially crosslinked polyolefin elastomer.

According to the invention, the polymer matrix constituting component“a” has a “melt flow index” (MFI), defined by the ASTM D 1238L standard(230° C. and 2.16 kg) lying between 5 and 100 g in 10 minutes andpreferably lying between 25 and 70 g in 10 minutes and a flexuralelastic modulus (FEM), defined by the ASTM D70 standard, at least equalto 20 MPa and preferably at least equal to 50 MPa.

The use of the various constituents of the aforementioned matrix in thecomposition according to the invention for slush moulding applicationleaves one to think that it might result in exudation of the lowmolecular masses of the elastomers present, which may represent up to10% by weight of the total mass. However, as soon as the composition ofthe matrix is chosen in such a way that its flexural elastic modulus isat least equal to 20 MPa and preferably at least equal to 50 MPa,exudation is accordingly diminished.

In prior polymer compositions (according to PCT InternationalApplication published under the number WO95/35344) comprisingelastomers, the exudation phenomenon was treated, often with onlypartial success, by means of agents such as resins chosen from the groupof elastomers of the ethylene-propylene-diene monomer (EPDM) orethylene-propylene rubber (EPR) type, these elastomers beinguncrosslinked or at least partially crosslinked and preferably combinedwith polypropylene, which resins have a melting range onset temperaturegreater than 140° C.

Should there still be a risk of subsequent exudation from the polymermatrix, it is possible, in order to eliminate this phenomenon, tocrosslink the various components by means of a suitable agent, such as aperoxide or a silane, or to chemically graft them by means of acrylicacid, methacrylic acid, alkyl acrylates or methacrylates, in which thealkyl is a C₁ to C₈ hydrocarbon chain, or maleic anhydride.

The matrix may be prepared by introducing at least one polymercontaining at least 50 mol % of propylene and at least one at leastpartially crosslinked elastomer into a reactor or into an extruder andby mixing them therein.

Various additives of known type and commonly used in compositionsintended for the slush moulding process may also be introduced into thecomposition according to the invention when preparing the mixture of theconstituents of the matrix, or even subsequently when preparing thecomposition according to the invention by the processing of its variousconstituents “a”, “b” and “c”.

These various additives are, for example, heat or photochemicalstabilizers, lubricants, antistatic agents, fire retardants,antioxidants, or yet others.

According to the invention, the thermoplastic polyolefin compositionhaving elastic properties also includes at least one polymer containingat least 50 mol % of ethylene constituting component “b”. This polymermay be low-density polyethylene (LDPE), linear low-density polyethylene(LLDPE), or else a blend of low-density polyethylene (LDPE) and ahigh-density polyethylene (HDPE), this blend containing at most 50% ofHDPE, or else an ethylene-alpha-olefin copolymer in which thealpha-olefin is a C3 to C10 unit, such as, more specifically,ethylene-octene copolymers (POE) comprising between 5 and 40% by weightof octene, ethylene terephthalate copolymers (PET), ethylene-vinylacetate copolymers (EVA), ethylene-alkyl acrylate copolymers orethylene-alkyl methacrylate copolymers in which the alkyl is a C1 to C8hydrocarbon chain, these being optionally modified by another monomersuch as, for example, maleic anhydride, a copolymer of ethylene and offluorocarbon monomer chosen among tetrafluoroethylene and fluorinatedethylene-propylene, or else ionomers which may or may not be in saltform. Preferably, the polymer containing at least 50 mol % of ethyleneconstituting component “b” has a melting range onset temperature at mostequal to 140° C.

The ethylene-monomer-based polymer constituting component “b” of thecomposition according to the invention allows the melting behaviour ofthe said composition to be substantially improved and results in afinalized product being obtained whose characteristics are close to thespecification usually imposed.

According to the invention, the thermoplastic polyolefin compositionhaving elastic properties may include at least one internalmould-release agent constituting component “c”.

The internal mould-release agent may be chosen from one of theconventionally known agents belonging to the group comprising the familyof montanic derivatives and montanic ester derivatives, stearate salts,amines, amides, hydrogenated hydrocarbon resins, polyethylene,polypropylene and ethylene/vinyl acetate copolymer (EVA) waxes, andaliphatic and/or aromatic monomer copolymerization resins.

Preferably, the internal mould-release agent may be chosen from thegroup formed by the alkaline-earth metal stearates, of which calciumstearate is the most used, and the amides of stearic acid(C17H35-CONH2), such as ethylene-bis-stearamide (EBS), these substancesbeing employed by themselves or as a blend.

The internal mould-release agent which, definitely, is preferably usedin the composition according to the invention is magnesium stearate, forwhich the Applicant has found experimentally that the phenomenon ofmigration through the skin previously observed does not occur, and thecharacteristics of which are:

magnesium stearate [Mg(C18H3502)2]: fine powder

bulk density: 0.2 g/litre

melting point: approximately 140 to 150° C.

rate of metal: 4.5 to 5.1.

Magnesium stearate used as an internal mould-release agent has manyadvantages, the most notable of which are mentioned below:

it easily replaces, by itself, the pair consisting of calciumstearate/ethyl-bis amide in which the ethyl-bis amide, which reduces themelt viscosity of the polymer composition containing them, promotes,excessively, the migration of the calcium stearate to the mould/materialinterface;

it is used, for the same reason as calcium stearate, as an antioxidantfor polypropylenes by limiting, or even preventing, thermo-oxidativedegradation of the polymer at the surface, this being the cause of areduction in the scratch, abrasion and solvent resistance properties;

its presence ensures excellent demoulding of the skin; and

it allows the skin to be lacquered with good adhesion of the lacquerafter a special preparation, such as flame brushing or the use of anadhesion primer.

The lacquering operation, if it is required, is usually carried out by aknown means, such as by depositing a thin layer of polyurethane on theexternal surface of the skin or else by chemical grafting on thesurface.

In practice, this lacquering operation has the purpose of substantiallyimproving certain properties of the skin such as, for example,increasing the abrasion resistance, scratch resistance and solventresistance, but also of allowing bonding of a paint, even locally, oradhesive bonding of an object having an aesthetically pleasingcharacter, for example.

The internal mould-release agent may be introduced into the compositionof the invention at the time of the mixing operation or when preparingthe matrix constituting component “a”, or else at the time when the saidmatrix is being mixed with the ethylene-based polymer constitutingcomponent “b”, when the latter is used.

The internal mould-release agent is introduced into the compositionpreferably in an amount of from 0.1 to 6 parts by weight and verypreferably in an amount of from 0.5 to 3 parts by weight per 100 partsby weight of components “a” and “b”.

The composition according to the invention is prepared according to amanufacturing process which consists:

in mixing the constituents of the composition in an extrusion zone; and

in cryogenically grinding the granules coming from the extrusion, insuch a way that this results in a thermoplastic polyolefin powder havingelastic properties.

Likewise, the composition according to the invention may be prepared bymicrogranulation, which consists of an extrusion through a microdie anda cutting at the level with the die in an aqueous medium, this resultingin a thermoplastic polyolefin powder having particles of almostspherical shape. The thermoplastic polyolefin powder according to theinvention, obtained according to an adapted process such as, forexample, those mentioned above, has a maximum particle size ofapproximately 400 μm and a median particle size of approximately 300 μmbut preferably approximately 250 μm.

Unlike the PVC particles used in the prior slush moulding processeswhich, coming from a fluidized-bed process, have a substantiallyspherical shape promoting the flow of the powder when charging themould, the thermoplastic polyolefin compositions, after they have beencryogenically ground, consist of microscopic particles which may haveangular shapes.

This is why, in order to ensure better flow over the mould of the powderresulting from the cryogenic grinding of the composition according tothe invention, to avoid local overcharging with this composition,whatever the shape of the mould, to charge the backtapers with powderand to decrease the thickness of the skins to be produced, it isdesirable to introduce into the composition according to the invention aflow agent for powders of polyolefin compositions coming from cryogenicgrinding and intended for the slush moulding process.

This flow agent is desirably a precipitated silica, of spherical shape,or an alumina, optionally grafted on the surface by a silane or by asilicone oil. If the precipitated silica or the alumina are grafted,they have the property of lowering, at discrete points, the meltviscosity of the composition and thus of penetrating more easily intothe skin and of being well dispersed therein.

The amount of flow agent used in the composition according to theinvention is between 0.1 and 10 parts and preferably between 0.1 and 5parts by weight per 100 parts by weight of components “a” and “b”.

By way of illustration, a precipitated and grafted silica, sold byDegussa under the reference SIPERNAT D10, used in the compositionaccording to the invention as a flow agent, has the followingproperties:

white, loose, hydrophobic powder

BET specific surface area (DIN 66131 standard): 90 m2/g

average diameter of the agglomerates: 5 μgm

compacted density (DIN-ISO 787/XI standard): 100 g/l.

Certain pulverulent mineral substances may also be introduced into thecomposition according to the invention; they may be chosen from mineralsalts and/or oxides which may or may not have undergone a surfacetreatment, such as calcium carbonate, magnesium carbonate, zinccarbonate, dolomite, lime, magnesia, aluminium trihydroxide, alumina,clays, preferably talc, kaolin, mica, bentonite, wollastonite and glassfibres and balls.

Finally, other organic pulverulent substances of natural or syntheticorigin may also be introduced, such as, for example, colorants, carbonblack or a finely ground polypropylene wax.

All these pulverulent substances may be used by themselves or incombination, and optionally introduced during the extrusion beforegranulation (compounding).

The dimensions of these mineral substances are generally between 0.01and 300 μm and preferably between 0.1 and 100 μm.

These pulverulent mineral substances may be introduced into thecompositions according to the invention in an amount of from 0.1 to 10parts and preferably from 0.1 to 5 parts by weight per 100 parts byweight of components “a” and “b”.

The compositions according to the invention may be prepared in a reactoror by extrusion or by powder-powder blending. Furthermore, they may becrosslinked by a peroxide or a silane or they may be grafted by acrylicacid, methacrylic acid, maleic anhydride or alkyl acrylates ormethacrylates in which the alkyl is a C1 to C8 hydrocarbon chain.

The composition according to the invention is processed using the slushmoulding process in order to produce skins intended to equip foam orunfoamed inserts such as, for example, dashboards, which meet, throughtests, the most demanding requirements of motor-vehicle manufacturers.

If the composition does not contain an internal mould-release agent, themould-release agent may be an external one and, in this case, it isdeposited directly on the surface of the mould. This externalmould-release agent may be chosen from the group consisting of thefamily of silicones, aliphatic and aromatic naphthas, polyphosphatidesand oils well known to those skilled in the art.

However, in addition, the mould-release agent, whether internal orexternal, may be replaced by a surface treatment of the mould whichmakes it a non-stick surface.

The invention will be more clearly understood by virtue of theillustrative and non-limiting examples described below.

EXAMPLE 1

This example illustrates a composition according to the invention usedsubsequently in the manufacture of foamed dashboards.

The various components making up the composition according to theinvention were as follows:

component “a”: polymer matrix: 70 parts by weight of a blend ofpolypropylene and elastomer, composed of:

60 parts by weight of REXFLEX 2330 polypropylene sold by Rexene;

10 parts by weight of SANTOPRENE 121-50 M 100 sold by AES, composed ofcompletely crosslinked EPDM and polypropylene;

component “b”: ethylene-octene copolymer containing 25% octene (ENGAGE,reference SM 8400 from Dow Chemical): 30 parts by weight; and

component “c”: mould-release agent (magnesium stearate): 0.2 parts byweight per 100 parts of “a” and “b”.

Added to this mould-release agent was a flow agent, in an amount of 0.3parts by weight per 100 parts of “a” and “b”, this being a precipitatedsilica of spherical shape onto which a silicone oil is grafted.

All these components, excluding the flow agent, were introduced into atwin-screw extruder which produced granules from the mixture of thesevarious components. The granules thus prepared were cryogenically ground(in the presence of liquid nitrogen) at a temperature of between −40° C.and −70° C.

The polyolefin thermoplastic composition according to the inventioncollected from the said grinding was in the form of a fine powder whosemedian particle size was approximately 250 μgm and whose maximumparticle size was approximately 350 μm.

The aforementioned flow agent was introduced, into the powder resultingfrom the cryogenic grinding, by means of a high-speed (Henschel) mixer.

Tests on the flow of the powder and on the production of skins by meansof this powder were carried out using a nickel mould heated to atemperature of between 200° C. and 240° C. and have made it possible toobtain good-quality skins, of uniform thickness (1 mm), for thedashboard to be foamed.

Foamed dashboards were then produced and subjected to qualificationtests for motor-vehicle manufacturers—they met the specifications.

EXAMPLE 2

This example illustrates another composition according to the invention,used subsequently in the manufacture of unlacquered foamed dashboards.

The various components making up the composition according to theinvention were as follows:

component “a”: polymer matrix: 90 parts by weight of a blend ofpolypropylene and elastomer, composed of:

70 parts by weight of REXFLEX D400 polypropylene sold by Rexene;

20 parts by weight of SANTOPRENE 121-50 M 100 sold by AES, composed ofcompletely crosslinked EPDM and polypropylene;

component “b”: ethylene-octene copolymer containing 25% octene (ENGAGE,reference SM 8400 from Dow Chemical): 10 parts by weight; and

component “c”: internal mould-release agent; 0 parts.

A flow agent was used in an amount of 0.2 parts by weight per 100 partsof “a” and “b”. This agent is a precipitated silica, of spherical shape,onto which a silicone oil is grafted, to which agent 0.5 parts by weightof a silica sold by Degussa under the reference SIPERNAT 22S was added.

All these components, excluding the flow agent, were introduced into atwin-screw extruder which produced granules from the mixture of thesevarious components. The granules thus prepared were cryogenically ground(in the presence of liquid nitrogen) at a temperature of between −40° C.and −70° C.

The polyolefin thermoplastic composition according to the inventioncollected from the said grinding was in the form of a fine powder whosemedian particle size was approximately 250 μm and whose maximum particlesize was approximately 350 μm.

The aforementioned flow agent was introduced, into the powder resultingfrom the cryogenic grinding, by means of a high-speed (Henschel) mixer.

Tests on the flow of the powder and on the production of skins by meansof this powder were carried out on a nickel mould heated to atemperature of between 200° C. and 240° C. and treated with an externalmould-release agent (ZYVAX sold by Diatex). These tests made it possibleto obtain good-quality skins, of uniform thickness (1 mm), fordashboards to be foamed.

Foamed dashboards were then produced and subjected to qualificationtests for motor-vehicle manufacturers—they came very close to meetingthe specifications.

EXAMPLE 3

This example also illustrates a composition according to the invention,used subsequently in the manufacture of non-pretreated unlacqueredfoamed dashboards.

The various components making up the composition according to theinvention were as follows:

component “a”: polymer matrix: 70 parts by weight of a blend ofpolypropylene and elastomer, composed of:

50 parts by weight of HIFAX CA131G polypropylene sold by Montell;

20 parts by weight of SANTOPRENE 121-50 M 100 sold by AES, composed ofcompletely crosslinked EPDM and polypropylene;

component “b”: ethylene-alkyl acrylate-maleic anhydride copolymer(LOTADER from Atochem): 30 parts by weight; and

component “c”: mould-release agent: 0 parts.

A flow agent was used in an amount of 0.2 parts by weight per 100 partsof “a” and “b”, this being a precipitated silica, of spherical shape,onto which a silicone oil is grafted, to which agent 0.5 parts by weightof a silica sold by Degussa under the reference SIPERNAT 22S was added.

All these components, excluding the flow agent, were introduced into atwin-screw extruder which produced granules from the mixture of thesevarious components. The granules thus prepared were cryogenically ground(in the presence of liquid nitrogen) at a temperature of between −40° C.and −70° C.

The polyolefin thermoplastic composition according to the inventioncollected from the said grinding was in the form of a fine powder whosemedian particle size was approximately 250 μm and whose maximum particlesize was approximately 350 μm.

The aforementioned flow agent was introduced, into the powder resultingfrom the cryogenic grinding, by means of a high-speed (Henschel) mixer.

Tests on the flow of the powder and on the production of skins by meansof this powder were carried out using a nickel mould heated to atemperature of between 200° C. and 240° C. and have made it possible toobtain good-quality skins, of uniform thickness (1 mm), for thedashboard to be foamed.

Foamed dashboards were then produced and subjected to qualificationtests for motor-vehicle manufacturers—they also came very close tomeeting the specifications.

What is claimed is:
 1. A polyolefin thermoplastic composition havingelastic properties, being in the form of a powder, intended for theproduction of skins, by slush molding, which contains fractions, onebeing formed of a propylene-based homopolymer or copolymer, anotherbeing formed of an ethylene-based copolymer and the final one beingformed of an elastomer, characterized in that it is composed of: a) from97 to approximately 5 parts by weight of a matrix composed of at leastone semi-crystalline polymer containing at least 50 mol % of propyleneand of at least one at least partially crosslinked polyolefin elastomer;b) from 3 to approximately 95 parts by weight of at least onenon-crosslinked polymer containing at least 50 mol % of ethylene; and c)from 0 to 6 parts by weight of an internal mold-release agent per 100parts by weight of components “a” and “b”; and is free of mineral oilbased softening agents.
 2. A thermoplastic composition according toclaim 1, characterized in that the polymer matrix “a” is composed of,expressed in % by weight: from 5 to 95% and preferably from 80 to 20% byweight of at least one semi-crystalline polymer containing at least 50mol % of propylene; and from 95 to 5% and preferably from 20 to 80% byweight of at least one at least partially crosslinked polyolefinelastomer.
 3. A composition according to claim 1, characterized in thatsemi-crystalline polymer containing at least 50 mol % of propylene ofthe polymer matrix “a” is chosen from the group consisting ofsemicrystalline homopolymer polypropylene, a semicrystallinepropylene-ethylene copolymer, a blend of semicrystalline homopolymerpolypropylene and of a semicrystalline propylene-ethylene copolymer,(homopolymer) polypropylene having amorphous and semicrystalline blocks,and propylene-ethylene or alpha-olefin copolymers having amorphous andsemicrystalline blocks.
 4. A composition according to claim 1,characterized in that the at least partially crosslinked polyolefinelastomer of the polymer matrix “a” is one of the elastomers belongingto the group consisting of ethylene-propylene rubber (EPR),ethylene-propylene-diene-monomer (EPDM), styrene-butadiene-styrene(SBS), styrene-ethylene-butadiene-styrene (SEBS) and styrene-butadienerubber (SBR).
 5. A composition according to claim 1, characterized inthat the at least partially crosslinked polyolefin elastomer of thepolymer matrix “a” is a blend of polypropylene with at least one of theelastomers ethylene-propylene rubber (EPR) and ethylene-propylene-dienemonomer (EPDM), the elastomeric fraction of which is at least partiallycrosslinked.
 6. A composition according to claim 1, characterized inthat the components of the polymer matrix “a” are chemically grafted bymeans of acrylic acid, methacrylic acid, maleic anhydride and alkylacrylates or methacrylates in which the alkyl is a C1 to C8 hydrocarbonchain.
 7. A composition according to claim 1, characterized in that thepolymer containing at least 50 mol % of ethylene forming the constituent“b” is chosen from the group consisting of low-density polyethylene(LDPE), linear low-density polyethylene (LLDPE), a blend of low-densitypolyethylene (LDPE) and a high-density polyethylene (HDPE), this blendcontaining at most 50% of HDPE, an ethylene-alpha-olefin copolymer inwhich the alpha-olefin is a C₃ to C₁₀ unit and, more specifically,ethylene-octene copolymers (POE) comprising between 5 and 40% by weightof octene, ethylene terephthalate copolymers (PET), ethylene-vinylacetate copolymers (EVA), ethylene-alkyl acrylate copolymers in whichthe alkyl is a C₁ to C₈ hydrocarbon chain optionally modified by maleicanhydride, a copolymer of ethylene and of fluorocarbon monomer chosenamong tetrafluoroethylene and fluorinated ethylene-propylene, andionomers optionally in salt form.
 8. A composition according to claim 7,characterized in that the polymer containing at least 50 mol % ofethylene forming constituent “b” has a melting range onset temperatureat most equal to 140° C.
 9. A composition according to claim 1,characterized in that the internal mould-release agent forming component“c” is from the family of montanic derivatives and montanic esterderivatives, stearate salts, amines, amides, hydrogenated hydrocarbonresins, polyethylene, polypropylene and ethylene/vinyl acetate copolymer(EVA) waxes, and aliphatic and/or aromatic monomer copolymerizationresins.
 10. A composition according to claim 1, characterized in thatthe internal mould-release agent forming component “c” is chosen fromthe group formed by alkaline-earth metal stearates, including calciumstearate, and the amides of stearic acid (C17H35-CONH2), includingethylene-bis-stearamide (EBS), these substances being employed bythemselves or as a blend.
 11. A composition according to claim 1,characterized in that the internal mould-release agent forming component“c” is magnesium stearate.
 12. A composition according to claim 9,characterized in that the internal mould-release agent is introduced inan amount of from 0.1 to 6 parts by weight and very preferably in anamount of from 0.5 to 3 parts by weight per 100 parts by weight ofcomponents “a” and “b”.
 13. A composition according to claim 1,characterized in that it also includes additives which are heat orphotochemical stabilizers, lubricants, antistatic agents, fireretardants and antioxidants.
 14. A composition according to claim 1,characterized in that it includes a flow agent.
 15. A compositionaccording to claim 14, characterized in that the flow agent is aprecipitated silica of spherical shape or an alumina optionally graftedon the surface by a silane or by a silicone oil.
 16. A compositionaccording to claim 14, characterized in that the amount of flow agent isbetween 0.1 and 10 parts and preferably between 0.1 and 5 parts byweight per 100 parts by weight of components “a” and “b”.
 17. Acomposition according to claim 1, characterized in that it containspulverulent mineral substances chosen from mineral salts and/or oxides,which may or may not have undergone a surface treatment, belonging tothe group consisting of calcium carbonate, magnesium carbonate, zinccarbonate, dolomite, lime, magnesia, aluminium trihydroxide, alumina,clays, preferably talc, kaoline, mica, bentonite, wollastonite, andglass fibres and balls.
 18. A composition according to claim 1,characterized in that it contains pulverulent organic substances ofnatural or synthetic origin which are chosen from the group ofcolorants, carbon black or a ground polypropylene wax.
 19. A compositionaccording to claim 17, characterized in that the pulverulent substancesare employed by themselves or as a mixture.
 20. A composition accordingto claim 17, characterized in that the size of the pulverulent mineralsubstances is between 0.01 and 300 μm and preferably between 0.1 and 100μm.
 21. A composition according to claim 17, characterized in that thepulverulent mineral substances are introduced in an amount of from 0.1to 10 parts and preferably from 0.1 to 5 parts by weight per 100 partsby weight of components “a” and “b”.
 22. A composition according toclaim 1, characterized in that it is crosslinked by means of a peroxideor a silane.
 23. A composition according to claim 1, characterized inthat it is grafted by means of acrylic acid, methacrylic acid, maleicanhydride or alkyl acrylates or methacrylates, in which the alkyl is aC1 to C8 hydrocarbon chain.
 24. Process for manufacturing a compositionaccording to claim 1, characterized in that: the constituents of thecomposition are mixed in an extrusion zone; the granules of the mixtureare cryogenically ground under conditions such that a maximum powderparticle size of about 400 μm is obtained.
 25. Process for manufacturinga composition according to claim 1, characterized in that it involvesmicrogranulation by extrusion through a microdie and a cutting at thelevel with the die in an aqueous medium.
 26. Moulded articles from acomposition according to claim
 1. 27. A polyolefin thermoplasticcomposition having elastic properties, being in the form of a powder,intended for the production of skins, by slush molding, which containsfractions, one being formed of a propylene-based homopolymer orcopolymer, another being formed of an ethylene-based copolymer and thefinal one being formed of an elastomer, characterized in that it iscomposed of: a) from 97 to approximately 5 parts by weight of a matrixcomposed of at least one semi-crystalline polymer containing at least 50mol % of propylene and of at least one at least partially crosslinkedpolyolefin elastomer; b) from 3 to approximately 95 parts by weight ofat least one non-crosslinked polymer containing at least 50 mol % ofethylene; and c) from 0 to 6 parts by weight of an internal mold-releaseagent per 100 parts by weight of components “a” and “b” which is free ofagents having high vapor pressures and which is free of mineral oilbased softening agents.
 28. A polyolefin thermoplastic compositionhaving elastic properties, being in the form of a powder, intended forthe production of skins, by slush molding, which contains fractions, onebeing formed of a propylene-based homopolymer or copolymer, anotherbeing formed of an ethylene-based copolymer and the final one beingformed of an elastomer, characterized in that it consists essentiallyof: a) from 97 to approximately 5 parts by weight of a matrix composedof at least one semi-crystalline polymer containing at least 50 mol % ofpropylene and of at least one at least partially crosslinked polyolefinelastomer; b) from 3 to approximately 95 parts by weight of at least onenon-crosslinked polymer containing at least 50 mol % of ethylene; and c)from 0 to 6 parts by weight of an internal mold-release agent per 100parts by weight of components “a” and “b” which is free of agents havinghigh vapor pressures and which is free of mineral oil based softeningagents.
 29. A composition as in claim 1, which is free of PVCplasticizers.
 30. A polyolefin thermoplastic composition having elasticproperties, being in the form of a powder, intended for the productionof skins, by slush molding, characterized in that it contains: a) from97 to approximately 5 parts by weight of a matrix composed of at leastone semi-crystalline polymer containing at least 50 mol % of propyleneand of at least one at least partially crosslinked polyolefin elastomer;b) from 3 to approximately 95 parts by weight of at least one polymercontaining at least 50 mol % of ethylene; c) from 0 to 6 parts by weightof an internal mold-release agent per 100 parts by weight of components“a” and “b”, and d) which is free of mineral oil.
 31. A polyolefinthermoplastic composition having elastic properties, being in the formof a powder, intended for the production of skins, by slush molding,characterized in that it contains: a) from 97 to approximately 5 partsby weight of a matrix composed of at least one semi-crystalline polymercontaining at least 50 mol % of propylene and of at least one at leastpartially crosslinked polyolefin elastomer; b) from 3 to approximately95 parts by weight of at least one polymer containing at least 50 mol %of ethylene; and c) from 0 to 6 parts by weight of an internalmold-release agent per 100 parts by weight of components “a” and “b”;wherein the semi-crystalline polymer containing at least 50 mol % ofpropylene is selected from the group consisting of semi-crystallinepolypropylene homopolymer, semi-crystalline propylene-ethylenecopolymers, blends of semi-crystalline polypropylene homopolymer and ofsemi-crystalline propylene-ethylene copolymers, polypropylenehomopolymer having amorphous and semi-crystalline blocks, andpropylene-ethylene or alpha-olefin copolymers having amorphous andsemi-crystalline blocks, d) which is free of mineral oil.